Hcg not doubling, but heartbeat detected

Calla

I got an hcg level drawn when I was 5 weeks and then When I was 6 weeks. My doctor was concerned because my numbers were not increasing like they should be. They had be come in for an ultrasound at 6w3d to rule out ectopic pregnancy. There was a baby in the uterus with a strong heartbeat! I am currently 9w2d pregnant and am still so caught up on my hcg levels not doubling appropriately. My doctor does not seem to be concerned at all and says once they detect a heartbeat the hcg levels do not matter anymore. Has this ever happened to anyone and has had a positive outcome?! TIA!